Dissolving ICs could be used as medical implants

SAN FRANCISCO—Researchers from Tufts University and the University of Illinois at Urbana-Champaign (UIUC) say they have created tiny, biocompatible semiconductors that dissolve harmlessly into their surroundings after functioning for a precise amount of time.

The silk-silicon devices, called "transient electronics," could be used as medical implants that never need surgical removal, as well as environmental monitors and consumer electronics that can become compost rather than trash, according to the researchers.

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The futuristic devices incorporate silicon and magnesium—key components of conventional integrated circuits—in an ultrathin form that is then encapsulated in silk protein.

"Transient electronics offer robust performance comparable to current devices but they will fully resorb into their environment at a prescribed time—ranging from minutes to years, depending on the application," said Fiorenzo Omenetto, a professor of biomedical engineering at Tufts School of Engineering. "Imagine the environmental benefits if cell phones, for example, could just dissolve instead of languishing in landfills for years."

Omenetto is among the authors of a paper on the subject, titled, "A Physically Transient Form of Silicon Electronics," published in the Sept. 28 issue of the journal Science.

"While silicon may appear to be impermeable, eventually it dissolves in water," Omenetto said. The challenge is to make the electrical components dissolve in minutes rather than eons, he said.

The transient electronic circuits are only a few tens of nanometers thick, from transistors to interconnects, and readily dissolve in a small amount of water or body fluid and are harmlessly reabsorbed, according to the researchers. Controlling materials at these scales makes it possible to fine-tune how long it takes the devices to dissolve, they say.

The researchers successfully demonstrated the new platform by testing a thermal device designed to monitor and prevent post-surgical infection (demonstrated in a rat model) and also created a 64 pixel digital camera.

Device dissolution is controlled by sheets of silk protein in which the electronics are supported and encapsulated. Silk protein—extracted from silkworm cocoons— is among the strongest, most robust materials known. It's also fully biodegradable and biofriendly and is already used for some medical applications.

Omenetto and his Tufts colleagues say they have discovered how to adjust the properties of silk so that it degrades at a wide range of intervals.

In the future, the researchers envision more complex devices that could be adjustable in real time or responsive to changes in their environment, such as chemistry, light or pressure.